Gypsum-containing product and gypsum board

ABSTRACT

The invention provides a set gypsum-containing product having increased resistance to permanent deformation and a method for preparing it comprising forming a mixture of a calcium sulfate material, water, and an appropriate amount of one or more enhancing materials chosen from condensed phosphoric acids, each of which comprises 2 or more phosphoric acid units; and salts or ions of condensed phosphates, each of which comprises 2 or more phosphate units. The mixture is then maintained under conditions sufficient for the calcium sulfate material to form a set gypsum material.

This application is a divisional application of co-pending U.S.application Ser. No. 12/797,013, filed on Jun. 9, 2010, which is acontinuation application of U.S. application Ser. No. 12/190,203, filedon Aug. 12, 2008, now U.S. Pat. No. 7,758,980, which is a divisionalapplication of U.S. application Ser. No. 11/760,886, filed on Jun. 11,2007, now U.S. Pat. No. 7,425,236, which is a continuation applicationof U.S. application Ser. No. 10/920,687, filed Aug. 18, 2004, now U.S.Pat. No. 7,244,304, which is a continuation application of U.S.application Ser. No. 10/293,739, filed on Nov. 13, 2002, now U.S. Pat.No. 6,800,131, which is a divisional application of U.S. applicationSer. No. 09/960,127, filed on Sep. 21, 2001, which is abandoned, whichis a divisional application of U.S. application Ser. No. 09/138,355,filed on Aug. 21, 1998, now U.S. Pat. No. 6,342,284, which was acontinuation-in-part application of U.S. application Ser. No.08/916,058, filed Aug. 21, 1997, which is abandoned, all of whichpreceding applications are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a method and composition for preparing setgypsum-containing products, e.g., gypsum boards, reinforced gypsumcomposite boards, plasters, machinable materials, joint treatmentmaterials, and acoustical tiles, and methods and compositions forproducing them. More particularly, the invention concerns such setgypsum-containing products that have increased resistance to permanentdeformation (e.g., sag resistance) by employing one or more enhancingmaterials. Some preferred embodiments of the invention concern makingsuch products by hydration of calcined gypsum in the presence of anenhancing material that causes the set gypsum produced by such hydrationto have increased strength, resistance to permanent deformation (e.g.,sag resistance), and dimensional stability (e.g., non-shrinkage duringdrying of set gypsum). The enhancing material also provides otherimproved properties and advantages in preparing the setgypsum-containing products. In an alternative embodiment of theinvention, set gypsum is treated with one or more enhancing materials toprovide similar, if not the same, increased strength, resistance topermanent deformation (e.g., sag resistance), dimensional stability, andother improved properties and advantages in gypsum-containing products.In some embodiments of the invention the set gypsum-containing productof the invention contains relatively high concentrations of chloridesalts, yet avoids detrimental effects of such salt concentrations ingypsum-containing products in general.

BACKGROUND

Many well known useful products contain set gypsum (calcium sulfatedihydrate) as a significant, and often as the major, component. Forexample, set gypsum is the major component of paper-faced gypsum boardsemployed in typical drywall construction of interior walls and ceilingsof buildings (see, e.g., U.S. Pat. Nos. 4,009,062 and 2,985,219). It isalso the major component of gypsum/cellulose fiber composite boards andproducts, as described in U.S. Pat. No. 5,320,677. Products that filland smooth the joints between edges of gypsum boards often contain majoramounts of gypsum (see, e.g., U.S. Pat. No. 3,297,601). Acoustical tilesuseful in suspended ceilings can contain significant percentages of setgypsum, as described, for example, in U.S. Pat. Nos. 5,395,438 and3,246,063. Traditional plasters in general, e.g., for use to createplaster-surfaced internal building walls, usually depend mainly on theformation of set gypsum. Many specialty materials, such as a materialuseful for modeling and mold-making that can be precisely machined asdescribed in U.S. Pat. No. 5,534,059, contain major amounts of gypsum.

Most such gypsum-containing products are prepared by forming a mixtureof calcined gypsum (calcium sulfate hemihydrate and/or calcium sulfateanhydrite) and water (and other components, as appropriate), casting themixture into a desired shaped mold or onto a surface, and allowing themixture to harden to form set (i.e., rehydrated) gypsum by reaction ofthe calcined gypsum with the water to form a matrix of crystallinehydrated gypsum (calcium sulfate dihydrate). This is often followed bymild heating to drive off the remaining free (unreacted) water to yielda dry product. It is the desired hydration of the calcined gypsum thatenables the formation of an interlocking matrix of set gypsum crystals,thus imparting strength to the gypsum structure in the gypsum-containingproduct.

All of the gypsum-containing products described above could benefit ifthe strength of their component set gypsum crystal structures wereincreased in order to make them more resistant to the stresses they mayencounter during use.

Also there is a continuing effort to make many such gypsum-containingproducts lighter in weight by substituting lower density materials(e.g., expanded perlite or air voids) for part of their set gypsummatrix. In such cases there is a need to increase the strength of theset gypsum above normal levels just to maintain overall product strengthat the levels of the previously higher density product, because there isless set gypsum mass to provide strength in the lower density product.

Furthermore, there is a need for greater resistance to permanentdeformation (e.g., sag resistance) in the structure of many of thesegypsum-containing products, especially under conditions of high humidityand temperature, or even load. The human eye typically cannot perceivesag of a gypsum-containing board at less than about 0.1 inch of sag pertwo foot length of board. Thus, there is a need for gypsum-containingproducts that are resistant to permanent deformation over the usefullife of such products. For example, gypsum-containing boards and tilesare often stored or employed in a manner in which they are positionedhorizontally. If the set gypsum matrix in these products is notsufficiently resistant to permanent deformation, especially under highhumidity and temperature, or even load, the products may start to sag inareas between the points where they are fastened to or supported by anunderlying structure. This can be unsightly and can cause difficultiesin use of the products. In many applications gypsum-containing productsmust be able to carry loads, e.g., insulation or condensation loads,without perceptible sag. Thus, there is a continuing need to be able toform set gypsum having increased resistance to permanent deformation(e.g., sag resistance).

There is also a need for greater dimensional stability of set gypsum ingypsum-containing products during their manufacture, processing, andcommercial application. Especially under conditions of changingtemperature and humidity, set gypsum can shrink or expand. For example,moisture taken up in crystal interstices of a gypsum matrix of a gypsumboard or tile exposed to high humidity and temperature can aggravate asagging problem by causing the humidified board to expand. Also, in thepreparation of set gypsum products there is usually a significant amountof free (unreacted) water left in the matrix after the gypsum has set.This free water is usually subsequently driven off by mild heating. Asthe evaporating water leaves the crystal interstices of the gypsummatrix, the matrix tends to shrink from natural forces of the set gypsum(i.e., the water was holding apart portions of the interlocking setgypsum crystals in the matrix, which then tend to move closer togetheras the water evaporates).

If such dimensional instability could be avoided or minimized, variousbenefits would result. For example, existing gypsum board productionmethods would yield more product if the boards did not shrink duringdrying, and gypsum-containing products desired to be relied on to hold aprecise shape and dimensional proportions (e.g., for use in modeling andmold making) would serve their purposes better. Also, for example, someplasters intended for interior building wall surfaces could benefit fromnot shrinking during drying, so that the plaster could be applied inthicker layers without danger of cracking, rather than needing to beapplied in multiple thinner layers with long pauses to allow adequatedrying between layer applications.

Some particular types of gypsum-containing products also exhibit otherparticular problems. For example, lower density gypsum-containingproducts are often produced by using foaming agents to create aqueousbubbles in calcined gypsum slurries (flowable aqueous mixtures) thatyield corresponding permanent voids in the product when the set gypsumforms. It is often a problem that, because the aqueous foams employedare inherently unstable and therefore many of the bubbles may coalesceand escape the relatively dilute slurry (like bubbles in a bubble bath)before the set gypsum forms, significant concentrations of foamingagents have to be employed to produce the desired concentration of voidsin the set gypsum, in order to obtain a product of desired density. Thisincreases costs and risks of adverse effects of chemical foaming agentson other components or properties of the gypsum-containing products. Itwould be desirable to be able to reduce the amount of foaming agentneeded to produce a desired void concentration in set gypsum-containingproducts.

There is also a need for new and improved compositions and methods forproducing set gypsum-containing products made from mixtures containinghigh concentrations (i.e., at least 0.015 weight percent, based on theweight of calcium sulfate materials in the mixture) of chloride ions orsalts thereof. The chloride ions or salts thereof may be impurities inthe calcium sulfate material itself or the water (e.g., sea water orbrine-containing subsurface water) employed in the mixture, which priorto the present invention could not be used to make stable setgypsum-containing products.

There is also a need for new and improved compositions and methods fortreating set gypsum to improve strength, resistance to permanentdeformation (e.g., sag resistance), and dimensional stability.

Thus, there is a continuing need for new and improved setgypsum-containing products, and compositions and methods for producingthem, that solve, avoid, or minimize the problems noted above. Thepresent invention meets these needs.

SUMMARY OF THE INVENTION

The present inventors have unexpectedly found set gypsum-containingproducts and compositions and methods for their preparation thatunexpectedly meet the needs described above. Each embodiment of theinvention meets one or more of these needs.

A set gypsum-containing product of the invention having increasedresistance to permanent deformation is prepared in accordance with theinvention by forming a mixture of a calcium sulfate material, water, andan appropriate amount of one or more enhancing materials chosen from:condensed phosphoric acids, each of which comprises 2 or more phosphoricacid units; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units.

The mixture is then maintained under conditions sufficient for thecalcium sulfate material to form the improved set gypsum material.

As used herein, the term, “calcium sulfate material”, is intended tomean calcium sulfate anhydrite; calcium sulfate hemihydrate; calciumsulfate dihydrate; ions of calcium and sulfate; or mixtures of any orall thereof.

In some embodiments of the invention the calcium sulfate material ismostly calcium sulfate hemihydrate. In such cases all of the enhancingmaterials described above will impart increased resistance to permanentdeformation to the set gypsum formed. However, some enhancing materials(e.g., the following salts, or the anionic portions thereof: sodiumtrimetaphosphate (also referred to herein as STMP), sodiumhexametaphosphate having 6-27 repeating phosphate units (also referredto herein as SHMP), and ammonium polyphosphate having 1000-3000repeating phosphate units (also referred to herein as APP)) will providepreferred benefits, such as greater increase in sag resistance. Also,APP provides equal sag resistance to that provided by STMP, even whenadded in only one fourth the STMP concentration.

In some preferred embodiments of the present invention, this isaccomplished by adding trimetaphosphate ion to a mixture of calcinedgypsum and water to be used to produce set gypsum-containing products(as used herein, the term, “calcined gypsum”, is intended to mean alphacalcium sulfate hemihydrate, beta calcium sulfate hemihydrate,water-soluble calcium sulfate anhydrite, or mixtures of any or allthereof, and the terms, “set gypsum” and “hydrated gypsum”, are intendedto mean calcium sulfate dihydrate). When the water in the mixture reactsspontaneously with the calcined gypsum to form set gypsum, the setgypsum is unexpectedly found to have increased strength, resistance topermanent deformation (e.g., sag resistance), and dimensional stability,compared with set gypsum formed from a mixture containing notrimetaphosphate ion. The mechanism for these improvements in propertiesis not understood.

Furthermore, it has been unexpectedly found that trimetaphosphate ion(like APP) does not retard the rate of the formation of set gypsum fromcalcined gypsum. In fact, when added at relatively higher concentrationlevels within its useful ranges of addition, trimetaphosphate ionactually accelerates the rate of hydration of calcined gypsum to formset gypsum. This is especially surprising, as is the increase in thestrength of the set gypsum, because it has been generally thought in thegypsum art that phosphoric or phosphate materials retard the rate offormation of set gypsum and decrease the strength of the gypsum formed.This is in fact true for most such materials, but not fortrimetaphosphate ion.

Thus, in general, some preferred embodiments of the invention provide amethod for producing a set gypsum-containing product having increasedstrength, resistance to permanent deformation (e.g., sag resistance),and dimensional stability, comprising: forming a mixture of calcinedgypsum, water, and trimetaphosphate ion, and maintaining the mixtureunder conditions (e.g., a temperature preferably less than about 120 F)sufficient for the calcined gypsum to convert to set gypsum.

In some preferred embodiments of the invention the method is one ofproducing a gypsum board comprising a core of set gypsum sandwichedbetween cover sheets of paper or other material. The board is preparedby forming a flowable mixture (slurry) of calcined gypsum, water, andtrimetaphosphate ion, depositing it between cover sheets, and allowingthe resultant assembly to set and dry.

While the board thus produced has all of the desired improved propertiesof increased strength, resistance to permanent deformation (e.g., sagresistance), and dimensional stability, it has been observed that, forreasons unknown, when such a board has for some reason become wet or hasnot been completely dried during production, the bond between the gypsumcore and the cover sheets (usually comprising paper) can lose strengthor even fail, even when the board contains a typical nonpregelatinizedstarch (e.g., an acid-modified starch) which normally contributes tobetter paper-to-core bond integrity. The cover sheets could thendelaminate from the board, which would be unacceptable. Fortunately thepresent inventors have also found a solution to this possible attendantproblem. They have found that the problem can be avoided by including apregelatinized starch in the production slurry. This starch then becomesdistributed throughout the resultant gypsum core, and it has beenunexpectedly found that this avoids the weakening of the bonding betweenthe core and the cover sheets.

Thus, in some of its embodiments the invention provides a compositionand method for producing an even more improved gypsum board. Thecomposition comprises a mixture of water, calcined gypsum,trimetaphosphate ion, and a pregelatinized starch. The method comprisesforming such a mixture, depositing it between cover sheets and allowingthe resultant assembly to set and dry.

In cases where it is desired to produce a gypsum board of lighterweight, the invention provides a composition and method foraccomplishing this. The composition comprises a mixture of water,calcined gypsum, trimetaphosphate ion, and an aqueous foam, and themethod comprises forming such a mixture, depositing it between coversheets, and allowing the resultant assembly to set and dry. Suchcomposition and method provide a board of lighter weight, because thebubbles of aqueous foam result in corresponding air voids in the setgypsum core of the resultant board. The overall strength of the board ishigher than a prior art board produced with the inclusion of an aqueousfoam in the mixture, because of the increased strength provided by theinclusion of the trimetaphosphate ion in the mixture used to form theinventive board. For example, ceiling boards of ½ inch thickness made inaccordance with the present invention have greater resistance topermanent deformation (e.g., sag resistance) than ______ inch ceilingboards made using prior art compositions and methods. Thus, the presentinvention provides substantial cost savings for ceiling boardproduction.

Unexpectedly, there has been found to be another benefit to theinclusion of trimetaphosphate ion in mixtures also containing an aqueousfoam. Namely, it has been found that proportionally more air voids (andmore overall air void volume) per unit amount of aqueous foam employed,are created in the resultant gypsum-containing product whentrimetaphosphate ion is included in the mixture. The reason for this isnot known, but the beneficial result is that less foaming agent has tobe employed to produce the desired amount of air void volume in the setgypsum-containing product. This in turn results in lower productioncosts and less risk of adverse effects of chemical foaming agents onother components or properties of the gypsum-containing product.

In some embodiments the invention provides a composite board comprisingset gypsum and a reinforcing material, prepared by: forming ordepositing a mixture on a surface, wherein the mixture comprises thereinforcing material, a calcium sulfate material, water, and anappropriate amount of one or more enhancing materials chosen fromcondensed phosphoric acids, each of which comprises 2 or more phosphoricacid units; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate material to form aset gypsum material.

The invention also provides a composite board comprising set gypsum andhost particles, at least a portion of the set gypsum being positioned inand about accessible voids in the host particles. The board is preparedby forming or depositing a mixture on a surface, wherein the mixturecomprises: the host particles; calcium sulfate hemihydrate, at least aportion of which is in the form of crystals in and about the voids ofthe host particles; water; and an appropriate amount of one or moreenhancing materials chosen from the group consisting of condensedphosphoric acids, each of which comprises 2 or more phosphoric acidunits; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate hemihydrate to formset gypsum, whereby the portion of the set gypsum in and about theaccessible voids in the host particles forms by in situ hydration of thecalcium sulfate hemihydrate crystals in and about the voids of the hostparticles.

The invention also provides a set gypsum-containing machinable productprepared by forming a mixture comprising a starch, particles of awater-redispersible polymer, a calcium sulfate material, water, and anappropriate amount of one or more enhancing materials chosen from:condensed phosphoric acids, each of which comprises 2 or more phosphoricacid units; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate material to form aset gypsum material.

The invention also provides a set gypsum-containing product employed tofinish a joint between edges of gypsum boards, the product prepared byinserting into the joint a mixture comprising a binder, a thickener, anon-leveling agent, a calcium sulfate material, water, and anappropriate amount of one or more enhancing materials chosen fromcondensed phosphoric acids, each of which comprises 2 or more phosphoricacid units; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate material to form aset gypsum material.

The invention also provides a set gypsum-containing acoustical tileprepared by forming or depositing in a tray a mixture comprising agelatinized starch, a mineral wool, a calcium sulfate material, water,and an appropriate amount of one or more enhancing materials chosen fromcondensed phosphoric acids, each of which comprises 2 or more phosphoricacid units; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate material to form aset gypsum material.

The invention also provides another type of set gypsum-containingacoustical tile prepared by forming or depositing in a tray a mixturecomprising a gelatinized starch, expanded perlite particles, a fiberreinforcing agent, a calcium sulfate material, water, and an appropriateamount of one or more enhancing materials chosen from condensedphosphoric acids, each of which comprises 2 or more phosphoric acidunits; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units. The mixture is then maintainedunder conditions sufficient for the calcium sulfate material to form aset gypsum material.

The invention also provides set gypsum-containing products made byforming a mixture of enhancing material, calcium sulfate dihydrate andwater. More specifically, these embodiments involve the treatment ofgypsum cast with enhancing material. Formation of a mixture of theenhancing material, water, and calcium sulfate dihydrate has been foundto provide set gypsum-containing products having increased strength,resistance to permanent deformation (i.e., sag resistance), anddimensional stability. Such post set treatment can be accomplished byaddition of the enhancing material by either spraying or soaking thecalcium sulfate dihydrate cast with the enhancing material.

In some embodiments the invention provides a composition and method forproducing set gypsum-containing products from mixtures containing highconcentrations of chloride ions or salts thereof (i.e., at least 0.015weight percent, based on the weight of calcium sulfate materials in themixture). The chloride ions or salts thereof may be impurities in thecalcium sulfate material itself or the water (e.g., sea water orbrine-containing subsurface water) employed in the mixture, which priorto the present invention could not be used to make stable setgypsum-containing products.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting product weight of gypsum board products,including the gypsum board of the present invention.

FIG. 2 is a graph comparing sag resistance of a gypsum board made inaccordance with the present invention with commercially available gypsumboards, wherein all the tested boards are installed using conventionalstapled and screwed ceiling attachment.

FIG. 3 is a graph comparing sag resistance of a gypsum board made inaccordance with the present invention with commercially available gypsumboards, wherein all the tested boards are installed using conventionalF2100 ceiling attachment (i.e., adhesive).

FIG. 4 is a graph comparing the sag deflection effect of a gypsum boardmade in accordance with the present invention and a commerciallyavailable gypsum board.

FIG. 5 is a graph depicting the sag deflection effect of treatment ofgypsum board in accordance with the present invention prepared fromgypsum board comprising previously set and dried gypsum (i.e., calciumsulfate dihydrate).

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention can be practiced employing compositions andmethods similar to those employed in the prior art to prepare variousset gypsum-containing products. The essential difference in thecompositions and methods of some preferred embodiments of this inventionfrom compositions and methods employed in the prior art to preparevarious set gypsum-containing products is that a trimetaphosphate saltis included to provide that in methods of the invention the rehydrationof calcined gypsum to form set gypsum takes place in the presence oftrimetaphosphate ion and thereby produces the benefits of the invention.In other respects the compositions and methods of the invention can bethe same as the corresponding compositions and methods of the prior art.

The trimetaphosphate salt included in compositions of the invention cancomprise any water-soluble trimetaphosphate salt that does not adverselyinteract with other components of the composition. Some examples ofuseful salts are sodium trimetaphosphate, potassium trimetaphosphate,ammonium trimetaphosphate, lithium trimetaphosphate, aluminumtrimetaphosphate, and mixed salts thereof, among others. Sodiumtrimetaphosphate is preferred. It is readily commercially available, forexample, from Solutia Inc. of St. Louis, Mo., previously a unit ofMonsanto Company of St. Louis, Mo.

To be used in the practice of one of the preferred methods of theinvention, the trimetaphosphate salt is dissolved in the aqueous mixtureof calcined gypsum to yield a trimetaphosphate ion concentration of fromabout 0.004 to about 2.0 percent by weight, based on the weight of thecalcined gypsum. A preferred concentration of trimetaphosphate ion isfrom about 0.04 to about 0.16 percent. A more preferred concentration isabout 0.08 percent. If desired for easier storage and delivery in thepractice of some embodiments of the invention, the trimetaphosphate saltcan be predissolved in water and inserted into the mixture in the formof an aqueous solution.

In accordance with a preferred embodiment of the invention, thetrimetaphosphate ion need only be present in the aqueous mixture ofcalcined gypsum during the hydration of the calcined gypsum to form setgypsum. Therefore, while it is usually most convenient and thuspreferred to insert the trimetaphosphate ion into the mixture at anearly stage, it is also sufficient to insert the trimetaphosphate ioninto the mixture of calcined gypsum and water at a somewhat later stage.For example, in preparing typical gypsum boards, water and calcinedgypsum are brought together in a mixing apparatus, are mixed thoroughly,and then are usually deposited onto a cover sheet on a moving belt, anda second cover sheet is placed over the deposited mixture before themajor part of the rehydration of calcined gypsum to form set gypsumoccurs. While it is most convenient to get the trimetaphosphate ion intothe mixture during its preparation in the mixing apparatus, it is alsosufficient to add the trimetaphosphate ion at a later stage, e.g., byspraying an aqueous solution of the ion onto the deposited aqueousmixture of calcined gypsum just before the second cover sheet is placedover the deposit, so that the aqueous trimetaphosphate ion solution willsoak into the deposited mixture and be present when the bulk of thehydration to form set gypsum occurs.

Other alternative methods of getting the trimetaphosphate ion into themixture will be apparent to those of ordinary skill in the art and areof course considered to be within the scope of the present invention.For example, it may be possible to pre-coat one or both of the coversheets with a trimetaphosphate salt, so that the salt will dissolve andcause trimetaphosphate ion to migrate through the mixture when thedeposit of the aqueous mixture of calcined gypsum comes into contactwith the cover sheet. Another alternative is to mix a trimetaphosphatesalt with raw gypsum even before it is heated to form calcined gypsum,so that the salt is already present when the calcined gypsum is mixedwith water to cause rehydration.

Other alternative methods of getting the trimetaphosphate ion into themixture are to add the trimetaphosphate ion to the set gypsum by anysuitable means, such as spraying or soaking the set gypsum with asolution containing trimetaphosphate. It has been found that thetrimetaphosphate ion will migrate to the set gypsum through conventionalpaper sheets used in the processing of set gypsum.

The calcined gypsum employed in the invention can be in the form andconcentrations typically found useful in the corresponding embodimentsof the prior art. It can be alpha calcium sulfate hemihydrate, betacalcium sulfate hemihydrate, water-soluble calcium sulfate anhydrite, ormixtures of any or all thereof, from natural or synthetic sources. Insome preferred embodiments alpha calcium sulfate hemihydrate is employedfor its yield of set gypsum having relatively high strength. In otherpreferred embodiments beta calcium sulfate hemihydrate or a mixture ofbeta calcium sulfate hemihydrate and water-soluble calcium sulfateanhydrite are employed.

Other conventional additives can be employed in the practice of theinvention in customary amounts to impart desirable properties and tofacilitate manufacturing, such as, for example, aqueous foam, setaccelerators, set retarders, recalcination inhibitors, binders,adhesives, dispersing aids, leveling or nonleveling agents, thickeners,bactericides, fungicides, pH adjusters, colorants, reinforcingmaterials, fire retardants, water repellants, fillers and mixturesthereof.

In some preferred inventive embodiments wherein the method andcomposition are for preparing gypsum board comprising a core of setgypsum-containing material sandwiched between cover sheets,trimetaphosphate ion is employed in the concentrations and mannerdescribed above. In other respects, the composition and method can bepracticed with the same components and in the same manner as thecorresponding compositions and methods for preparing gypsum board of theprior art, for example, as described in U.S. Pat. Nos. 4,009,062 and2,985,219, the disclosures of which are incorporated herein byreference. Boards produced using this preferred inventive compositionand method exhibit improved strength, resistance to permanentdeformation, and dimensional stability.

In preferred methods and compositions for preparing gypsum board,wherein the surface sheets of the board comprise paper, a pregelatinizedstarch is also employed to avoid the otherwise slightly increased riskof paper delamination under conditions of extreme moisture.Pregelatinizing of raw starch is achieved by cooking in water attemperatures of at least 185 F or by other well known methods.

Some examples of readily available pregelatinized starches that servethe purposes of the present invention are (identified by theircommercial names): PCF1000 starch, available from Lauhoff Grain Co.; andAMERIKOR 818 and HQM PREGEL starches, both available from Archer DanielsMidland Co.

To be used in a preferred practice of the invention, the pregelatinizedstarch is included in the aqueous mixture of calcined gypsum at aconcentration of from about 0.08 to about 0.5 percent by weight, basedon the weight of the calcined gypsum. A preferred concentration ofpregelatinized starch is from about 0.16 to about 0.4 percent. A morepreferred concentration is about 0.3 percent. If the correspondingembodiment of the prior art also contains a starch that has not beenpregelatinized (as many do), the pregelatinized starch in the inventiveembodiment can also serve to replace all or a portion of the amount ofthat prior art starch normally employed.

In embodiments of the invention that employ a foaming agent to yieldvoids in the set gypsum-containing product to provide lighter weight,any of the conventional foaming agents known to be useful in preparingfoamed set gypsum products can be employed. Many such foaming agents arewell known and readily available commercially, e.g., from GEO SpecialtyChemicals in Ambler, Pa. For further descriptions of useful foamingagents, see, for example: U.S. Pat. Nos. 4,676,835; 5,158,612; 5,240,639and 5,643,510; and PCT International Application Publication WO95/16515, published Jun. 22, 1995.

In many cases it will be preferred to form relatively large voids in thegypsum product, in order to help maintain its strength. This can beaccomplished by employing a foaming agent that generates foam that isrelatively unstable when in contact with calcined gypsum slurry.Preferably, this is accomplished by blending a major amount of foamingagent known to generate relatively unstable foam, with a minor amount offoaming agent known to generate relatively stable foam.

Such a foaming agent mixture can be pre-blended “off-line”, i.e.,separate from the process of preparing foamed gypsum product. However,it is preferable to blend such foaming agents concurrently andcontinuously, as an integral “on-line” part of the process. This can beaccomplished, for example, by pumping separate streams of the differentfoaming agents and bringing the streams together at, or just prior to,the foam generator that is employed to generate the stream of aqueousfoam which is then inserted into and mixed with the calcined gypsumslurry. By blending in this manner, the ratio of foaming agents in theblend can be simply and efficiently adjusted (for example, by changingthe flow rate of one or both of the separate streams) to achieve thedesired void characteristics in the foamed set gypsum product. Suchadjustment will be made in response to an examination of the finalproduct to determine whether such adjustment is needed. Furtherdescription of such “on-line” blending and adjusting can be found inU.S. Pat. No. 5,643,510, and in copending U.S. patent application Ser.No. 08/577,367, filed Dec. 22, 1995.

An example of one type of foaming agent, useful to generate unstablefoams, has the formula

ROSO₃ _(—) M⊕  (Q)

wherein R is an alkyl group containing from 2 to 20 carbon atoms, and Mis a cation. Preferably, R is an alkyl group containing from 8 to 12carbon atoms.

An example of one type of foaming agent, useful to generate stablefoams, has the formula

CH₃(CH₂)_(X)CH₂(OCH₂CH₂)_(Y)OSO₃ _(—) M⊕  (J)

wherein X is a number from 2 to 20, Y is a number from 0 to 10 and isgreater than 0 in at least 50 weight percent of the foaming agent, and Mis a cation.

In some preferred embodiments of the invention, foaming agents havingthe formulas (Q) and (J) above are blended together, such that theformula (Q) foaming agent and the portion of the formula (J) foamingagent wherein Y is 0, together constitute from 86 to 99 weight percentof the resultant blend of foaming agents.

In some preferred embodiments of the invention, the aqueous foam hasbeen generated from a pre-blended foaming agent having the formula

CH₃(CH₂)_(X)CH₂(OCH₂CH₂)_(Y)OSO₃ _(—) M⊕  (Z)

wherein X is a number from 2 to 20, Y is a number from 0 to 10 and is 0in at least 50 weight percent of the foaming agent, and M is a cation.Preferably, Y is 0 in from 86 to 99 weight percent of the formula (Z)foaming agent.

In some preferred inventive embodiments wherein the method andcomposition are for preparing a composite board comprising set gypsumand particles of a reinforcing material, trimetaphosphate ion isemployed in the concentrations and manner described above. It isparticularly preferred that the composite product comprise set gypsumand host particles, at least a portion of the set gypsum beingpositioned in and about accessible voids in the host particles. Theinventive composition comprises a mixture of: host particles havingaccessible voids therein; calcined gypsum, at least a portion of whichis in the form of crystals in and about the voids in the host particles;and a water-soluble trimetaphosphate salt. The composition can be mixedwith water to produce an inventive mixture of water, host particleshaving accessible voids therein, calcined gypsum (at least a portion ofwhich is in the form of crystals in and about the voids in the hostparticles), and trimetaphosphate ion. The method comprises forming sucha mixture, depositing it on a surface or into a mold, and allowing it toset and dry. In other respects, the composition and method can bepracticed with the same components and in the same manner as thecorresponding compositions and methods for preparing composite board ofthe prior art, for example, as described in U.S. Pat. No. 5,320,677, thedisclosure of which is incorporated herein by reference.

In some preferred inventive embodiments wherein the method andcomposition are for preparing a machinable material, trimetaphosphateion is employed in the concentrations and manner described above. Insome preferred forms of such embodiments the composition comprises amixture of calcined gypsum, a water-soluble trimetaphosphate salt, astarch, and particles of a water-redispersible polymer. The compositioncan be mixed with water to produce an inventive mixture of water,calcined gypsum, trimetaphosphate ion, starch, and particles ofwater-redispersible polymer. The method comprises forming such amixture, depositing it on a surface or into a mold, and allowing it toset and dry. In respect to aspects other than the inclusion oftrimetaphosphate salts and ions, the composition and method can bepracticed with the same components and in the same manner as thecorresponding compositions and methods for preparing machinable plastermaterial of the prior art, for example, as described in U.S. Pat. No.5,534,059, the disclosure of which is incorporated herein by reference.

In some preferred inventive embodiments wherein the method andcomposition are for producing a material employed to finish a jointbetween edges of gypsum boards, trimetaphosphate salt or ion is employedin the concentrations described above. In respect to aspects other thanthe inclusion of trimetaphosphate salts and ions, the composition andmethod can be practiced with the same components and in the same manneras the corresponding compositions and methods for producing a jointfinishing material in the prior art, for example, as described in U.S.Pat. No. 3,297,601, the disclosure of which is incorporated herein byreference. In some preferred forms of such embodiments the compositioncomprises a mixture of calcined gypsum, a water-soluble trimetaphosphatesalt, a binder, a thickener, and a non-leveling agent. The compositioncan be mixed with water to produce an inventive mixture of calcinedgypsum, trimetaphosphate ion, binder, thickener, and non-leveling agent.The method comprises forming such a mixture, inserting it into a jointbetween edges of gypsum boards, and allowing it to set and dry.

In such preferred joint finishing embodiments the binder, thickener, andnon-leveling agent are chosen from the components well known to thoseskilled in the joint compound art. For example, the binder can be aconventional latex binder, with poly(vinyl acetate) andpoly(ethylene-co-vinyl acetate) being preferred and being included in arange of from about 1 to about 15 percent by weight of the composition.An example of a useful thickener is a cellulosic thickener, e.g.,ethylhydroxy ethylcellulose, hydroxypropyl methylcellulose,methylhydroxypropyl cellulose, or hydroxyethyl cellulose, included in arange of from about 0.1 to about 2 percent by weight of the composition.Examples of suitable non-leveling agents are attapulgite, sepiolite,bentonite, and montmorillonite clays, included in a range of from about1 to about 10 percent by weight of the composition.

In some preferred inventive embodiments wherein the method andcomposition are for preparing an acoustical tile, trimetaphosphate ionis included in the concentrations described above. In some preferredforms of such embodiments the composition comprises a mixture of water,calcined gypsum, trimetaphosphate ion, a gelatinized starch, and mineralwool or a mixture of water, calcined gypsum, trimetaphosphate ion, agelatinized starch, expanded perlite particles, and a fiber reinforcingagent. The method comprises forming such a mixture, casting it into atray, and allowing it to set and dry. In respect to aspects other thanthe inclusion of trimetaphosphate ion, the composition and method can bepracticed with the same components and in the same manner as thecorresponding compositions and methods for producing an acoustical tileof the prior art, for example, as described in U.S. Pat. Nos. 5,395,438and 3,246,063, the disclosures of which are incorporated herein byreference.

The following examples are presented to further illustrate somepreferred embodiments of the invention and to compare them with methodsand compositions outside the scope of the invention. Unless otherwiseindicated, concentrations of materials in compositions and mixtures aregiven in percent by weight based upon the weight of calcined gypsumpresent. The abbreviation, “STMP”, stands for sodium trimetaphosphate,and the abbreviation, “TMP”, stands for trimetaphosphate.

Example 1 Laboratory Cube Compressive Strength

Samples of gypsum-containing products were prepared in accordance withthe invention and compared, in regard to compressive strength, withsamples prepared using different methods and compositions. The testprocedure employed was in accordance with ASTM C472-93.

Samples were prepared by dry blending: 500 g of beta calcium sulfatehemihydrate; 0.6 g of a set accelerator referred to as CSA (ClimateStable Accelerator) commercially available from United States GypsumCompany and comprising fine ground particles of calcium sulfatedihydrate coated to maintain efficiency; and 0 g additive (controlsamples), 0.5-2 g of STMP (preferred inventive samples), or 0.5-2 g ofother phosphate additives (comparative samples). The samples were thenmixed with 700 ml tap water having a temperature of 70 F in a 2 literWARING blender, allowed to soak for 5 seconds and mixed at low speed for10 seconds. The slurries thus formed were cast into molds to preparecubes (2 inches per side). After the calcium sulfate hemihydrate set toform gypsum (calcium sulfate dihydrate), the cubes were removed from themolds and dried in a ventilated oven at 112 F for at least 72 hours oruntil their weight stopped changing. The dried cubes had a density ofabout 44 pounds per cubic foot (pcf).

Each dry cube's compressive strength was measured on a SATEC testingmachine. Results are reported in TABLE 1, below, as average values ofthree tested samples. Strength values for control samples varied,because various sources of beta calcium sulfate hemihydrate and/ordifferent batches of beta calcium sulfate hemihydrate were employed.Results in the table are reported in the form of the measuredcompressive strength in pounds per square inch (psi) and percent changein strength over the relevant control (% Δ). Measured values areestimated to have an experimental error of about +/−5% (thus, a reportedstrength increase over the control of 10% may have actually beenanywhere in the range of 5-15%).

TABLE 1 Compressive Strength 0% 0.1% 0.2% additive additive additive0.4% additive 0.8% additive Additive (psi) (psi; %Δ) (psi; %Δ) (psi; %Δ)(psi; %Δ) STMP 987 1054; 6.8  1075; 8.9  1072; 8.6  — STMP 724 843; 16.4957; 32.2 865; 19.5 783; 8.1    STMP 742 819; 10.4 850; 14.6 — — STMP714 800; 12.0 834; 16.8 — — STMP 842 985; 17.0 1005; 19.4  1053; 25.1 611; −27.4 STMP 682 803; 17.7 826; 21.1 887; 30.1 — sodium 950 951; 0.1 929; −2.2 — — phosphate sodium 950 993; 4.5  873; −8.1 — — tripoly-phosphate sodium 950   845; −11.1  552; −41.9 — — hexameta- phosphatedicalcium 763 769; 0.8  775; 1.6  761; −0.3 — phosphate disodium 763757; −0.8 728; −4.6 700; −8.3 — phosphate monocalcium 763 786; 3.0  766;0.4  824; 8.0  — phosphate monohydrate

The data in TABLE 1 illustrate that the inventive samples (STMP)generally exhibited significantly increased strength over the controls,while the comparative samples generally showed very little or nostrength increase or even a significant strength decrease.

Example 2 Resistance to Permanent Deformation Laboratory Gypsum BoardSag Resistance

Samples of gypsum-containing boards were prepared in a laboratory inaccordance with the invention and compared, in regard to resistance topermanent deformation, with sample boards prepared using methods andcompositions outside the scope of the invention.

Samples were prepared by mixing in a 5 liter WARING blender for 10seconds at low speed: 1.5 kg of beta calcium sulfate hemihydrate; 2 g ofCSA set accelerator; 2 liters of tap water; and 0 g additive (controlsamples), 3 g of STMP (inventive samples), or 3 g of other additives(comparative samples). The slurries thus formed were cast into trays toprepare flat gypsum board samples, each having dimensions of about6×24×½ inches. After the calcium sulfate hemihydrate set to form gypsum(calcium sulfate dihydrate), the boards were dried in a 112 F oven untiltheir weight stopped changing. The final measured weight of each boardwas recorded. No paper facing was applied to these boards, in order toavoid the effect of paper covers on the gypsum boards' sag performanceunder humidified conditions.

Each dried board was then laid in a horizontal position upon two½-inch-wide supports whose length extended the full width of the board,with one support at each end of the board. The boards remained in thisposition for a specified period of time (in this example, 4 days) undercontinuous surrounding conditions of 90 F temperature and 90 percentrelative humidity. The extent of sag of the board was then determined bymeasuring the distance (in inches) of the center of the top surface ofthe board from the imaginary horizontal plane extending between the topedges of the ends of the board. The resistance to permanent deformationof the set gypsum matrix of the board is considered to be inverselyproportional to the extent of the sag of the board. Thus, the greaterthe extent of the sag is, the lower is the relative resistance topermanent deformation of the set gypsum matrix comprising the board.

The tests of resistance to permanent deformation are reported in TABLE2, including the composition and concentration (weight percent based onthe weight of calcium sulfate hemihydrate) of the additive, the finalweight of the board, and the extent of measured sag. The additivesemployed in the comparative samples (outside the scope of the invention)are representative of other materials that have been employed to attemptto improve resistance of gypsum board to sagging under conditions ofhigh humidity.

TABLE 2 Extent of Gypsum Board Sag Additive Board Board Sag Additive(weight %) Weight (g) (inches) none (control) 0 830 0.519 STMP 0.2 8380.015 boric acid 0.2 829 0.160 sodium aluminum 0.2 835 0.550 phosphatewax emulsion 7.5 718 0.411 glass fiber 0.2 838 0.549 glass fiber + boricacid 0.2 + 0.2 825 0.161

The data in TABLE 2 illustrate that the board (STMP) prepared inaccordance with the invention was much more resistant to sag (and thusmuch more resistant to permanent deformation) than the control board andthe noninventive comparative boards. Moreover, the board prepared inaccordance with the invention had sag that was much less than 0.1 inchof sag per two foot length of board, and thus not perceptible to thehuman eye.

Example 3 Resistance to Permanent Deformation Production Line GypsumBoard Sag Resistance

A product weight comparison is shown in FIG. 1, and the sag resistanceof such products is shown in FIGS. 2 and 3. The product weight ofinterior ½ inch ceiling board in accordance with the present invention(i.e., admixing trimetaphosphate with calcined gypsum and water) has thesame weight as interior ½ inch SHEETROCK® regular gypsum board made byUnited States Gypsum Company. The average ½ inch interior ceiling boardshown in FIG. 1 is Gold Bond® High Strength Ceiling Board made byNational Gypsum Company. The average ______ inch gypsum board shown inFIG. 1 is SHEETROCK®______ inch Firecode Type X gypsum board made byUnited States Gypsum Company.

FIG. 2 is a graph comparing sag resistance of a gypsum board made inaccordance with the present invention with commercially available gypsumboards described above, wherein all the tested boards are installedusing conventional stapled and screwed ceiling attachment.

FIG. 3 is a graph comparing sag resistance of a gypsum board made inaccordance with the present invention with commercially available gypsumboards described above, wherein all the tested boards are installedusing conventional F2100 Two-Part Urethane Adhesive ceiling attachment.

The gypsum boards and other construction details to make the ceilingsused in the sag comparisons depicted in FIGS. 2 and 3 were as follows:

-   A. Gypsum Board—    -   1. ½ inch×48 inch×96 inch made in accordance with the present        invention.    -   2. ½ inch×48 inch×96 inch National Gypsum Company Gold Bond®        High Strength Ceiling Board.    -   3. ½ inch×48 inch×96 inch regular SHEETROCK® gypsum board made        by United States Gypsum Company.    -   4. ______ inch×48 inch×96 inch SHEETROCK® Firecode Type X gypsum        board made by United States Gypsum Company.-   B. Trusses—18 inch tall×102 inch long manufactured from nominal 2    inch×3 inch lumber by R.J. Cole, Inc. Joint Compound—USG Tuff Set    HES Joint Compound. Joint Tape—USG Fiberglass Mesh Self-Adhering    Joint Tape.-   C. Vapor Barrier Paint—#4512 Silver Vapor Barrier, item: 246900.-   D. Insulation—Delta Blowing Insulation blowing wool, Rockwool    mineral fiber.-   E. Spray Texture—USG SHEETROCK® Ceiling Spray Texture Q T medium    poly.-   F. Fasteners—1 inch c.×1¼ inch lg.×Ga. staples, and #6×1¼ lg.    drywall screws. F2100 Two-part Urethane Adhesive from Foamseal, Inc.

Ceiling Construction

-   -   A. 2×4s were attached at both ends of the trusses to make a        truss framework.    -   B. Twelve (12) sheets of gypsum boards were attached to the        truss framework with F2100 adhesive. An average bead width of 1        inch was measured on the gypsum boards.    -   C. The ceiling was carefully raised and placed on top of four        walls previously constructed, to form an 8 foot×48 foot room.    -   D. The ceiling assembly was attached to the top plate of the        walls with #8×3½ inch screws around the perimeter. A second        ceiling was built using screws and staples to attach the gypsum        boards to the trusses. It was also raised up and attached to        four (4) walls.

Two (2) ceilings were built using three (3) sheets of each gypsum typeboard in each ceiling. The one ceiling was mechanically fastened (seeFIG. 2), while the other was fastened with F2100 urethane adhesive only(see FIG. 3). The gypsum boards were laid out, alternating gypsum boardtypes, along the ceilings. The trusses used were 8 foot 5 inch long by18 inch tall and were spaced at 24 inch on center (“o.c.”).

The mechanically fastened ceiling used 1 inch crown×1¼ inch lg.×16 Ga.staples at 7 inches o.c. along seams and #6×1¼ inch lg. drywall screwsat 12 inch o.c. along field trusses.

The adhesively attached ceiling used an approximate 1¼ inch bead alongtrusses. A bead was used on one side of field trusses and along a beadon both sides of trusses at gypsum seams.

The gypsum board was attached with the paper wrapped edges alignedparallel to the truss chords.

The initial position was measured after the gypsum seams were taped.Next the ceilings were painted with vapor barrier paint and then spraytextured. A second reading was taken immediately after texturing.Rockwool insulation was then blown into the top of the trusses. A thirdreading was then taken. The temperature and humidity were raised duringthe time the insulation was blown in. The target temperature andhumidity were 90° F. and 90% relative humidity. These conditions wereheld for seven (7) days while deflections were measured each morning andafternoon. After the seven days, the room was opened and brought down toambient temperature. Sag measurements were read for three (3) more days,and then the test was terminated.

As shown in FIGS. 2 and 3, gypsum boards made in accordance with thepresent invention provide significant sag resistance over other gypsumboards and were below the threshold of about 0.1 inch of sag per twofoot length of board perceptible to the human eye.

Example 4 Laboratory Gypsum Board Nail Pull Resistance

Laboratory prepared samples of typical paper-covered gypsum boardsproduced in accordance with the invention were compared with controlboards in regard to nail pull resistance. Nail pull resistance is ameasure of a combination of the strengths of the board's gypsum core,its paper cover sheets, and the bond between the paper and the gypsum.The test measures the maximum force required to pull a nail with a headthrough the board until major cracking of the board occurs, and iscarried out in accordance with ASTM C473-95.

Slurries were prepared by mixing in a HOBART mixer for 40 seconds at amedium speed: 3.0 kg of beta calcium sulfate hemihydrate; 5 g of CSA setaccelerator; 10 g of LC-211 starch (a dry-milled acid-modifiednon-pregelatinized wheat starch typically included in prior artformulations for gypsum board and commercially available from ArcherDaniels Midland Milling Co.); 20 g of fine hammermilled paper fiber; 3liters of tap water; 0-6 g of STMP; and 0-30 g of PCF1000 pregelatinizedcorn starch, commercially available from Lauhoff Grain Co.

The slurries thus formed were cast into trays on top of paper and thenhad paper applied to their top surface to prepare flat gypsum boardsamples, each having dimensions of about 14×24×½ inches. The paper onone surface was multi-ply with manila outer plies, and the paper on theother surface was multi-ply newsline, both typical of papers employed toprepare paper-covered gypsum board in the board industry. Each board wasthen held in a 350 F oven until it lost 25 percent weight and was thentransferred to and held in a 112 F oven until it reached constantweight.

Final board weight and nail pull resistance were measured. The resultsare reported in TABLE 3.

TABLE 3 Nail Pull Resistance STMP PCF1000 Board Nail Pull ConcentrationStarch Weight Resistance (weight %) (weight %) (lbs/1000 ft²) (lbs) 0 02465 150 0.1 0 2454 155 0.2 0 2326 158 0.1 0.5 2458 168 0.2 1.0 2495 176

The results in TABLE 3 show that boards prepared in accordance with theinvention exhibited higher overall strength (nail pull resistance)compared with control boards.

Example 5 Dimensional Stability and Resistance to Permanent Deformationof Production Line Gypsum Board

Paper-covered foamed gypsum boards were prepared on a typical full scaleproduction line in a commercial gypsum board manufacturing facility.Boards were prepared with various concentrations of trimetaphosphate ionand were compared with control boards (prepared without trimetaphosphateion) in regard to dimensional stability and resistance to permanentdeformation. Except for the inclusion of trimetaphosphate ion in thepreparation of some of the boards, the boards were prepared usingmethods and ingredients typical of prior art gypsum board productionmethods and ingredients. The ingredients and their approximate weightpercentages (expressed as relatively narrow ranges based upon the weightof calcined gypsum employed) are listed in TABLE 4.

TABLE 4 Gypsum Board Production Ingredients INGREDIENT WEIGHT % betacalcium sulfate hemihydrate 100 water 94-98 set accelerator 1.1-1.6starch 0.5-0.7 dispersant 0.20-0.22 paper fiber 0.5-0.7 set retarder0.07-0.09 foaming agent 0.02-0.03 sodium trimetaphosphate (“STMP”)  0-0.16 recalcination inhibitor 0.13-0.14

In TABLE 4: the set accelerator comprised finely ground sugar-coatedparticles of calcium sulfate dihydrate produced by United States GypsumCompany and referred to as “HRA” (which stands for heat resistantaccelerator); the starch was dry-milled acid-modified HI-BOND starchobtained commercially from Lauhoff Grain Co.; the dispersant wasDILOFLO, a naphthalene sulfonate obtained commercially from GEOSpecialty Chemicals of Ambler, Pa.; the paper fiber was finehammermilled paper fiber; the set retarder was VERSENEX 80, a chelatingagent obtained commercially from Van Walters & Rogers of Kirkland,Wash.; the foaming agent was WITCOLATE1276, obtained commercially fromWitco Corp. of Greenwich, Conn.; the sodium trimetaphosphate wassupplied commercially by Monsanto Co. of St. Louis, Mo.; and therecalcination inhibitor was CERELOSE 2001, a dextrose employed to reducerecalcination of board ends during drying.

The boards were produced on a four foot wide continuous production lineby: continuously introducing and mixing the ingredients in a mixer toform an aqueous slurry (the foaming agent was used to generate aqueousfoam in a separate foam generating system; the foam was then introducedinto the slurry through the mixer); continuously depositing the slurryon a paper cover sheet (face paper) on a moving belt; placing anotherpaper cover sheet (back paper) over the deposited slurry to form ½ inchthick board; when the hydration of the calcium sulfate hemihydrate toform calcium sulfate dihydrate proceeded far enough to make the slurryhard enough to cut precisely, cutting the moving board to makeindividual boards of about 12×4 feet and ½ inch thick; and drying theboards in a heated multideck kiln.

Resistance to permanent deformation of the boards was then determined bymeasuring sag as described in Example 2, except that the boards testedwere about 1 foot×4 foot (the 1 foot being in the production linedirection, i.e., parallel direction) sections cut from the productionboards. Measurement of sag was carried out after conditioning the boardsin an environment of 90 F temperature and 90% relative humidity for 24,48, and 96 hours. Results are reported in TABLE 5 for inventive samplesproduced with various concentrations of trimetaphosphate ion and controlsamples (0% sodium trimetaphosphate) produced immediately before andafter the inventive samples.

TABLE 5 Production Line Gypsum Board Sag (1 foot × 4 foot Board) STMPBoard Sag Board Sag Board Sag Concentration after 24 hrs. after 48 hrs.after 96 hrs. (weight %) (inches) (inches) (inches) 0 (before) 3.45 3.955.27 0.004 3.23 3.71 5.19 0.008 2.81 3.31 4.58 0.016 1.72 1.91 2.580.024 0.96 1.12 1.61 0.04 0.49 0.68 0.82 0.08 0.21 0.24 0.29 0 (after)3.65 4.58 6.75

The data in TABLE 5 illustrate that the boards prepared in accordancewith the invention were progressively more resistant to sag (and thusprogressively more resistant to permanent deformation) than the controlboards, as STMP concentration was increased.

The sag resistance provided by the compositions and methods of thepresent invention are further depicted in Table 5A. More specifically,Table 5A shows sag, i.e., humidified deflection in accordance ASTM C473-95, of a production line gypsum board having the dimensions of 1foot×2 foot and having the same formulation shown in above Table 4.Table 5A shows the same trends in sag resistance pursuant to ASTM C473-95 as the trends in the sag resistance for longer boards (1 foot×4foot) as shown in FIG. 5.

TABLE 5A Results of ASTM C 473-95 Humidified Deflection Test forProduction Line Gypsum Board STMP 48 Hours Humidified Addition Dry BoardDeflection (inch) f Test Number (wt %) Weight lb/MSF Parallel AcrossControl Before 0 1590 −0.306 −0.247 1 0.04 1583 −0.042 −0.034 2 0.081609 −0.027 −0.021 3 0.16 1583 −0.015 −0.014 Control After 0 1585 −0.409−0.145

Both wet 12×4 ft. production boards and final dried 12×4 ft. productionline boards were also measured (in accordance with ASTM C473-95) todetermine the amounts of shrinkage of their widths and lengths afterdrying. The more the boards shrink, the less is their dimensionalstability. The results are reported in TABLE 6.

TABLE 6 Production Line Gypsum Board Shrinkage STMP Board Width BoardLength Concentration Shrinkage Shrinkage (weight %) (inches/4 ft.)(inches/12 ft.) 0 (control) 0.13 0.38 0.004 0.06 0.38 0.008 0 0.31 0.0160 0.25 0.024 0 0.25 0.040 0 0 0.080 0 0 0.16 0 0

The data in TABLE 6 show that boards prepared in accordance with theinvention were more dimensionally stable than control boards. At 0.04%STMP addition and above, no length or width shrinkage was found.

Example 6 Sag Resistance Under Humidified and Condensation ConditionsProduction Line Gypsum Board

An additional test illustrates sag resistance provided by thecompositions and methods of the present invention. More specifically,production line ceiling board was tested wherein controlled condensationwas allowed to occur at a vapor barrier placed between the ceiling boardand the joists. The method for this test is as follows. A small scaleattic and room enclosure was constructed. The attic space was insulatedon its top and sides and kept cool to obtain controlled condensation atthe ceiling. The ceiling area was 8 foot×8 foot, with 2 foot×8 footframing and 24 inch o.c. The room space was enclosed by a 6 mil polyvapor barrier at its top and sides, and the humidity of the room spacewas elevated to obtain controlled condensation at the ceiling.

Two 4 foot×8 foot boards of test material (one trial product and onecontrol) were attached side-by-side to the trusses, with the 6 milpolyethylene vapor barrier located directly above the board. The ends ofthe board were not fastened. The humidity in the room portion was thenincreased via a vaporizing humidifier while the temperature in the atticwas lowered using a window air conditioning unit. The vapor output ofthe humidifier was adjusted until a constant condensation occurred atthe vapor barrier above the ceiling board. No attempt was made tomaintain constant temperature and humidity throughout the test. Theresults should therefore be viewed as a relative measure of sagresistance performance between the trial and control products, and notan attempt to predict the amount of sag in a defined conditionedenvironment.

Ceiling sag was then periodically measured for three locations along theboard (at midspan between each pair of trusses), giving a total of sixdeflection readings per product per test. The temperature of the atticand room enclosures were also recorded at each sag measurement.

For background information, the theoretical dew point conditions(assuming a constant 70° F. room temperature) are shown below.

Room Temp. Room Relative Humidity Attic Temp. 70° F. 50% 51° F. 70° F.60% 56° F. 70° F. 70% 60° F. 70° F. 80% 63° F. 70° F. 90% 68° F.

A test was performed over a nineteen day period using the followingmaterial: ½ inch product line gypsum board made in accordance with thepresent invention; and ______ inch Firecode Type X gypsum board aspreviously described. Results are shown in the FIG. 4 and show the boardmade in accordance with the present invention has consistently less sagthan the control, i.e., ______ inch Firecode Type X gypsum board aspreviously described.

In this test a distributed load of 1.0 lb/lineal foot was applied atmidspan between each truss immediately following the reading of Day 8.Application of this load significantly increased sag of the controlboard, but had much less effect on the board of the present invention.As shown in FIG. 4, gypsum boards made in accordance with the presentinvention have deflection of sag that is significantly below that whichis perceptible to the human eye, i.e., less than 0.1 inch per two footlength.

Example 7 Production Line Gypsum Board Nail Pull Resistance

Another set of paper-covered foamed gypsum boards was prepared on atypical full scale production line in a gypsum board manufacturingfacility. Boards were prepared with three concentrations oftrimetaphosphate ion and were compared with control boards (preparedwithout trimetaphosphate ion) in regard to nail pull resistance.

Except for the inclusion of trimetaphosphate ion in the preparation ofsome of the boards, the boards were prepared using methods andingredients typical of prior art gypsum board production methods andingredients. The ingredients and their weight percentages were the sameas those listed in TABLE 4 above. The method of preparation of theboards was as described in EXAMPLE 5.

Nail pull resistance was determined in accordance with ASTM C473-95.Results are reported in TABLE 7 for inventive samples produced withvarious concentrations of trimetaphosphate ion and control samples (0%sodium trimetaphosphate) produced immediately before and after theinventive samples.

TABLE 7 Production Line Gypsum Board Nail Pull Resistance STMP Nail PullConcentration Resistance (weight %) (lbs) 0 (before) 89 0.04 93 0.08 960.16 99 0 (after) 90

The results in TABLE 7 show that production boards prepared inaccordance with the invention exhibited higher overall strength (nailpull resistance) compared with control boards.

Example 8 Production Line Gypsum Board Paper Bond Integrity

Another set of paper-covered foamed gypsum boards was prepared on atypical full scale production line in a gypsum board manufacturingfacility. Boards were prepared with various concentrations oftrimetaphosphate ion, pregelatinized starch, and non-pregelatinizedstarch and were compared with control boards (prepared withouttrimetaphosphate ion or pregelatinized starch) in regard to theintegrity of the bond between the gypsum board core and its face coverpaper after conditioning under extremely wet and humidified conditions.

Except for the inclusion of trimetaphosphate ion and pregelatinizedstarch and the varying of the concentration of non-pregelatinized starchin the preparation of some of the boards, the boards were prepared usingmethods and ingredients typical of prior art gypsum board productionmethods and ingredients. The ingredients and their weight percentageswere the same as those listed in TABLE 4 above. The method ofpreparation of the boards was as described in EXAMPLE 5.

The pregelatinized starch employed in the tests was PCF1000,commercially available from Lauhoff Grain Co. The non-pregelatinizedstarch was HI-BOND, a dry-milled acid-modified non-pregelatinized starchcommercially available from Lauhoff Grain Co.

After production line preparation of the boards, samples with dimensionsof 4×6×½ inches (the 4 inches being in the production line direction)were cut from the boards. Each of these smaller board samples was thenconditioned by keeping the total area of the outer surface of the coverpaper on its face side in contact with a fully water-soaked cloth forabout 6 hours in an environment of 90 F temperature and 90 percentrelative humidity and then removing the wet cloth and allowing the boardsample to slowly dry in that same environment until it reached constantweight (usually about 3 days). A one eighth inch-deep straight score wasthen made in the rear surface of the board sample 2½ inches from andparallel to one of the 6 inch edges. The board core was then snappedalong the score without breaking or stressing the paper on the face sideof the board, and the larger (2½×6 inches) piece of the board sample wasthen rotated and forced downward while the smaller piece was heldstationary and horizontally with its rear surface up, in an attempt toforce the face paper on the face side of the board to peel away from thelarger piece. The force was increased until the two board pieces camecompletely apart. The face surface of the larger piece was then examinedto determine on what percentage of its surface the face paper had pulledcompletely away from the core (referred to as “clean peel”). Thispercentage is reported in TABLE 8 as the “% Bond Failure”.

TABLE 8 Production Line Gypsum Board Paper Bond Failure HI-BOND STMPPCF1000 % Bond Concentration Concentration Concentration Failure (weight%) (weight %) (weight %) (%) 0.60 0 0 87 0.60 0.08 0 97 0.96 0.08 0 970.60 0.08 0.16 42 0.60 0.08 0.32 0 0.28 0.08 0.32 20 0.60 0 0 83

The data in TABLE 8 show that in regard to the problem of paper-to-corebond failure after extremely wet conditioning: STMP aggravates theproblem; increasing the concentration of typical non-pregelatinizedstarch (HI-BOND) does not alleviate the problem; adding somepregelatinized starch (PCF1000) alleviates or eliminates the problem.

Example 9 Post Treatment of Calcium Sulfate Dihydrate

In some alternative preferred embodiments of the present invention,calcium sulfate dihydrate cast is treated with an aqueous solution oftrimetaphosphate ion, in a manner sufficient to uniformly disperse thesolution of trimetaphosphate ion in the calcium sulfate dihydrate cast,to increase strength, resistance to permanent deformation (e.g., sagresistance), and dimensional stability of set gypsum-containing productsafter redrying. More specifically, treatment of calcium sulfatedihydrate cast with trimetaphosphate ion has been discovered to increasestrength, resistance to permanent deformation (e.g., sag resistance) anddimensional stability to an extent similar to that achieved by theembodiments wherein trimetaphosphate ion is added to calcined gypsum.Thus, the embodiment wherein the trimetaphosphate ion is added to setgypsum provides new compositions and methods for making improvedgypsum-containing products, including but not limited to boards, panels,plasters, tiles, gypsum/cellulose fiber composites, etc. Therefore, anygypsum based product which requires strict control over sag resistancewill benefit from this embodiment of the present invention. Thetreatment also increases gypsum cast strength by ˜15%. Trimetaphosphateion can be loaded at 0.04-2.0% (based on gypsum weight) into gypsum castby spraying or soaking with an aqueous solution containingtrimetaphosphate ion and then redrying the gypsum cast.

Two methods of post treatment of set gypsum are as follows.

In both of the above methods, the aqueous solution of trimetaphosphateion is preferably applied in an amount and manner sufficient to create aconcentration of about 0.04-0.16% by weight (based on the weight ofcalcium sulfate dihydrate) of trimetaphosphate ion in the calciumsulfate dihydrate cast.

Benefits of reduction in sag deflection (i.e., sag resistance) of thefirst method above are shown in FIG. 5. Five (5) boards were made andtested for sag deflection as shown in FIG. 5. The dried boards weighedin the range of 750 to 785 grams. The control boards did not have anysolution applied to them after gypsum cast/final set and dry. The boardidentified as the water only board had only water applied as a spray tothe set and dried gypsum cast, and was then redried. The boardidentified as the STMP solution board had a 1 wt. % trimetaphosphate ionaqueous solution applied as a spray to the set and dried gypsum cast,and was then redried. The board identified as Gyp-STMP solution had anaqueous mixture saturated with gypsum and containing 1% by weighttrimetaphosphate ion applied as a spray to the set and dried gypsumcast, and was then redried. In general, it is preferred to have thesolution to be sprayed contain a concentration of trimetaphosphate ionin the range of 0.5% to 2%. The final amount of trimetaphosphate ion inboth the STMP solution board and the Gyp-STMP solution board was 0.2%based on weight of stucco used to make the gypsum cast and 0.17% basedon weight of the resulting set gypsum board.

Example 10 Treatment of High Salt Materials

Other embodiments the invention concern set gypsum-containing productsprepared from mixtures of calcium sulfate materials and water containinghigh concentrations of chloride ions or salts thereof (i.e., at least0.015 weight percent, based on the weight of calcium sulfate materialsin the mixture). The chloride ions or salts thereof may be impurities inthe calcium sulfate material itself or the water (e.g., sea water orbrine-containing subsurface water) employed in the mixture, which priorto the present invention could not be used to make stable setgypsum-containing products because of attendant problems, such asblisters, paper bond failure, end burning, low resistance to permanentdeformation, low strength, and low dimensional stability.

The tests included in Table 9 concern gypsum boards prepared and treatedin the same manner as described in Example 2, except that variousamounts of chloride ion were introduced into the mixture along withvarious amounts of trimetaphosphate ion. The sag deflection was testedin the same manner as described in Example 2.

TABLE 9 Lab test results of gypsum cubes (2 × 2 × 2)/board core (24 × 6× 0.5) cast from stucco with various STMP & sodium chloride additionCompressive Sodium Chloride STMP Dry Board Water Pick-Up 48 HrsHumidified Strength Addition Addition Weight from 90/90 Room SagDeflection Of Dried Cubes (wt. %) (wt. %) (grams) (wt. %) (inches) (psi)0 0 534 0.17 0.445 675 0.2 0 535 0.88 2.086 697 0.5 0 528 1.91 4.086 6031.0 0 500 4.74 >6 448 2.0 0 481 6.94 >6 304 0.5 0 530 1.90 3.752 613 0.50.1 526 1.94 0.006 678 0.5 0.2 527 1.92 0.007 684 0.5 0.3 518 1.95 0.005662 0.5 0.5 508 1.89 0.003 668 0.8 0 509 2.93 5.786 477 0.8 0.1 509 3.070.014 540 0.8 0.2 505 2.91 0.007 543 0.8 0.4 501 2.99 0.010 538 0.8 0.8500 2.96 0.005 554

The tests included in Table 10 show that treatment with trimetaphosphateion permits the use of mixtures containing high concentrations ofchloride ions or salts thereof. The boards were prepared and treated inthe same manner as in Example 4, except that various amounts of chlorideion were introduced into the mixture along with various amounts oftrimetaphosphate ion. The integrity of the bond between the gypsum boardcore and its face cover paper was tested in the same manner as describedin Example 8.

TABLE 10 Paper-to-core bond test results of lab cast gypsum board (24 ×14 × 0.5) cast from stucco at various STMP, PCF 1000 & LC-211starch, andsalt addition 3 Hrs Wet & PCF1000 Dry Water Pick-up 5 Days Humidified 3Days Humidified Salt STMP & LC-211 Board After 5 Days Bond BondHumidified Bond Addition Addition Addition Weight in 90/90 Room FailureFailure Bond Failure (wt. %) (wt. %) (wt. %) (grams) (wt. %) (%) (%)Failure (%) (%) 0 0 0.2 & 0.2 2271 0.29 0 5 0 2 0.2 0 0.2 & 0.2 22900.81 1 0 0 0 0.6 0 0.2 & 0.2 2284 2.12 2 8 0 0 0.2 0.1 0.2 & 0.2 22690.87 0 1 2 1 0.6 0.1 0.2 & 0.2 2267 1.95 2 3 0 0 0.6 0.2 0.2 & 0.2 22712.07 3 0 3 2 1.0 0.2 0.2 & 0.2 2285 3.61 9 14 3 10

Table 11 shows treatment with trimetaphosphate ion and PFC 1000 starchof high chloride salt materials (0.08 to 0.16 wt. % of sodium chloridein stucco) of boards that were otherwise prepared and treated in amanner similar to that previously described in Example 5. As shown inTable 11, the treatment results in an increase in nail pull strength(measured in the same manner as Example 4, i.e., ASTM C 473-95) andprovides similar bond performance (measured in the same manner asExample 8) as compared with control boards with no sodium chloride.Further, trimetaphosphate ion treatment provided significant improvementin humidified sag, even up to 0.3% chloride salt addition.

TABLE 11 PLANT TEST RESULTS OF HIGH-SALT TRIAL AT GYPSUM PILOT FACILITYNaCl Salt STMP Hi-Bond PCF 1000 Board Nail Pull Paper to Core Bond 24Hrs. Humidified Sag Trial Addition Addition Starch Starch WeightStrength % Fail (1′ × 4′) Period (wt. %) (wt. %) (wt. %) (wt. %)(lb/MSF) (lb) Load (lb) (%) (inches/4 ft span)  1 (Control) 0 0 0.52 01581 88.7 14.8 13.6 3.25 2 0 0 0.28 0.24 1586 92.1 13.30 15.3 2.45 30.08 0 0.28 0.24 1577 89.3 11.20 13.7 5.25 4 0.16 0 0.28 0.24 1580 87.711.50 22.4 11.5 5 0.3 0 0.28 0.24 1574 89.6 9.00 31.8 >12.5 6 0.3 0.080.28 0.24 1577 89.2 8.10 30.3 0.25 7 0.16 0.08 0.28 0.24 1567 95.5 11.4032.8 0.25 8 0.08 0.08 0.28 0.24 1592 94.5 12.20 19.5 0.25 9 0 0 0.280.24 1609 93.6 12.40 15.1 2.85 10 (Control) 0 0 0.52 0 1561 83.9 14.9011.5 2.25 11  0.3 0 0.52 0 1619 93.4 10.10 25.4 >12.5

Table 12 shows treatment with trimetaphosphate ion and PFC 1000 starchof even higher (than shown in Table 11) chloride salt materials (0.368wt. % of chloride salt in stucco) of boards that were otherwise preparedand treated in a manner similar to that previously described in Example5. As shown in Table 12, the treatment results in an increase in nailpull strength (measured in the same manner as Example 4, i.e., ASTM C473-95) and provides better bond performance (measured in the samemanner as Example 8) as compared with control boards.

TABLE 12 PLANT TEST RESULTS OF HIGH-SALT TRIAL AT BOARD PLANT PCF-Paper-to- % High-Chloride Chloride Salt STMP Hi-Bond 1000 Nail Pull CoreBond Trial Synthetic Gypsum Concentration Addition Starch StarchStrength Load % Fail Period (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (lb)(lb) (%) 1 (Control) 0 0.032 0 0.4 0 73 14.10 49.0 2 50 0.12 0.16 0.150.25 85 16.70 0.0 3 100 0.368 0.16 0.15 0.25 86 14.40 0.0 4 100 0.3680.16 0.4 0 89 10.90 34.0 5 100 0.368 0 0.4 0 77 19.70 0.0 6 (Control) 00.032 0 0.4 0 75 19.5 10.0

Example 11 Treatment of Calcined Gypsum with Various Enhancing Materials

In the example of the preferred embodiments previously discussed, theenhancing material is trimetaphosphate ion. However, in general, anyenhancing materials that fall within the general definition of enhancingmaterials previously discussed will produce beneficial results (e.g.,increased resistance to permanent deformation) in treatment of calcinedgypsum. The generally useful enhancing materials are condensedphosphoric acids, each of which comprises 2 or more phosphoric acidunits; and salts or ions of condensed phosphates, each of whichcomprises 2 or more phosphate units.

Specific examples of such enhancing materials include, e.g., thefollowing acids or salts, or the anionic portions thereof: sodiumtrimetaphosphate having the molecular formula (NaPO₃)₃, sodiumhexametaphosphate having 6-27 repeating phosphate units and having themolecular formula Na_(n+2)P_(n)O_(3n+1) wherein n=6-27, tetrapotassiumpyrophosphate having the molecular formula K₄P₂O₇, trisodium dipotassiumtripolyphosphate having the molecular formula Na₃K₂P₃O₁₀, sodiumtripolyphosphate having the molecular formula Na₅P₃O₁₀, tetrasodiumpyrophosphate having the molecular formula Na₄P₂O₇, aluminumtrimetaphosphate having the molecular formula Al(PO₃)₃, sodium acidpyrophosphate having the molecular formula Na₂H₂P₂O₇, ammoniumpolyphosphate having 1000-3000 repeating phosphate units and having themolecular formula (NH₄)_(n+2)P_(n)O_(3n+1) wherein n=1000-3000, orpolyphosphoric acid having 2 or more repeating phosphoric acid units andhaving the molecular formula H_(n+2)P_(n)O_(3n+1) wherein n is 2 ormore.

Results of using such enhancing materials to treat calcined gypsum areshown in Tables 13, 14, and 15.

In Table 13 various enhancing materials were used to treat calcinedgypsum in the process of preparing gypsum boards and cubes. The boardswere prepared and treated in the same manner as previously in describedin Example 2. The cubes were prepared and treated in the same manner aspreviously described in Example 1. Except in both cases, variousdifferent enhancing materials were used rather than justtrimetaphosphate ion. Humidified sag deflection was measured in the samemanner as previously described in Example 2. Compressive strength wasmeasured in the same manner as previously described in Example 1.

In Table 14 polyphosphoric acid was used to treat calcined gypsum in theprocess of preparing gypsum boards and cubes. The boards were preparedand treated in the same manner as previously in described in Example 2.The cubes were prepared and treated in the same manner as previouslydescribed in Example 1. Except in both cases, various differentenhancing materials were used rather than just trimetaphosphate ion.Humidified sag deflection was measured in the same manner as previouslydescribed in Example 2. Compressive strength was measured in the samemanner as previously described in Example 1.

In Table 15 ammonium polyphosphate (“APP”) was used to treat calcinedgypsum in the process of preparing gypsum boards and cubes. The boardswere prepared and treated in the same manner as previously in describedin Example 2. The cubes were prepared and treated in the same manner aspreviously described in Example 1. Except in both cases, variousdifferent enhancing materials were used rather than justtrimetaphosphate ion. Humidified sag deflection was measured in the samemanner as previously described in Example 2. Compressive strength wasmeasured in the same manner as previously described in Example 1.

The results in Tables 13, 14, and 15 show that all materials tested thatare within the definition of enhancing materials above, when used totreat calcined gypsum in the production of set gypsum-containingproducts, cause the products to exhibit significant resistance topermanent deformation compared with the controls.

TABLE 13 Lab test results of gypsum cubes (2 × 2 × 2) and boards (24 × 6× 0.5) cast from stucco with various phosphate & chloride additionAddition Dry Board Retard (−), Water Pick-Up Ten Day CompressivePhosphate Salts Level Weight Neutral (0) or from 90/90 Humidified SagStrength of Dried Or Other Specified Chemicals (wt. %) (gram) Accelerate(+) Room (wt. %) Deflection (inches) Cubes (psi) Sodium Trimetaphosphate0.1 537.0 0/+ 0.06 0.016 745 Sodium Hexametaphosphate 0.1 538.2 −− 0.090.019 552 Sodium Chloride & Sodium Trimetaphosphate 0.5 & 0.1 527.5 +1.93 0.008 621 Sodium Chloride & Sodium 0.5 & 0.1 539.6 −/0 2.08 0.021498 Hexametaphosphate Tetrapotassium Pyrophosphate 0.1 538.7 −/0 0.110.137 560 Trisodium Dipotassium Tripolyphosphate 0.1 538.8 −/0 0.070.201 552 Sodium Tripolyphosphate 0.1 535.1 −/0 0.09 0.286 531Tetrasodium Pyrophosphate 0.1 556.2 −/0 0.18 0.436 544 AluminumTrimetaphosphate 0.1 536.2 0/0 0.02 0.521 673 MonopotassiumDihydrogenPhosphate 0.1 540.9 0/+ 0.11 0.595 657 Sodium AcidPyrophosphate 0.1 547.7 0/0 0.16 1.385 637 Boric Acid 0.1 539.4 0/0 0.151.425 624 Trisodium Phosphate 0.1 537.0 −− 0.13 1.641 537 Control 0.0546.2 0/0 0.13 1.734 635 Phosphoric Acid 0.1 534.0 + 0.22 1.796 673Monosodium DihydrogenPhosphate 0.1 540.9 + 0.19 2.219 679 MagnesiumChloride 0.1 528.2 0/+ 0.23 2.875 521 Disodium MonohydrogenPhosphate 0.1536.6 0/0 0.13 3.126 629 Sodium Aluminum Sulfate 0.1 543.0 ++ 0.24 3.867686 Zinc Chloride 0.1 536.2 0/+ 0.67 >6.0 470 Aluminum Chloride 0.1536.8 +++ 0.53 >6.0 464 Sodium Chloride 0.1 542.6 + 0.63 >6.0 596

TABLE 14 Lab test results of gypsum cubes (2 × 2 × 2)/boards (24 × 6 ×0.5) cast from stucco with polyphosphoric acid addition Water Pick- TwoWeeks Compressive Addition Dry Board Retard (−), Up from HumidifiedStrength Of Level Weight Neutral (0) or 90/90 Room Sag Deflection DriedCubes Polyphosphoric Acid (wt. %) (gram) Accelerate (+) (wt. %) (inches)(psi) No Phosphoric Acid (Control) 0.0 536.5 0/0 0.06 0.683 767Polyphosphoric acid (mixing with water first) 0.02 539.6 0/0 0.13 0.042781 Polyphosphoric acid (mixing with water first) 0.05 535.1 0/0 0.090.025 842 Polyphosphoric acid (mixing with water first) 0.1 542.3 −/00.15 0.046 708

TABLE 15 Lab test results of gypsum cubes (2 × 2 × 2)/boards (24 × 6 ×0.5) cast from stucco with ammonium polyphosphate addition Water Pick-UpTwo Weeks Compressive Addition Dry Board Retard (−), from HumidifiedStrength Of Level Weight Neutral (0) or 90/90 Room Sag Deflection DriedCubes Ammonium Polyphosphate (“APP”) (wt. %) (gram) Accelerate (+) (wt.%) (inches) (psi) Control 0.0 540.7 0/0 0.35 0.694 912 APP Powder(mixing with water first) 0.01 532.5 0/0 0.35 0.045 937 APP Powder(mixing with water first) 0.03 536.3 0/0 0.37 0.020 924 APP Powder(mixing with water first) 0.05 539.7 0/0 0.37 0.005 901 APP Powder(mixing with water first) 0.1 541.3 0/0 0.28 0.005 956 APP Powder(mixing with water first) 0.2 546.7 0/0 0.30 0.003 967 APP Powder(mixing with water first) 0.4 538.2 0/0 0.33 0.005 998 APP Powder(mixing with stucco first) 0.05 533.5 0/0 0.35 0.005 907 APP Powder(mixing with stucco first) 0.1 546.9 0/0 0.30 0.006 948 APP Powder(mixing with stucco first) 0.2 538.3 0/0 0.31 0.006 998 APP Powder(mixing with stucco first) 0.4 537.4 0/0 0.35 0.002 1017

Example 12 Treatment of Calcium Sulfate Dihydrate Cast with VariousEnhancing Materials

In general, any enhancing materials that fall within the generaldefinition of enhancing materials previously discussed will producebeneficial results (e.g., increased resistance to permanent deformation,and increased strength) in treatment of calcium sulfate dihydrate cast.The generally useful enhancing materials are condensed phosphoric acids,each of which comprises 2 or more phosphoric acid units; and salts orions of condensed phosphates, each of which comprises 2 or morephosphate units.

Results of using such enhancing materials to treat calcium sulfatedihydrate cast are shown in Table 16.

In Table 16 various different materials were used to treat set and driedcalcium sulfate dihydrate in the form of boards and cubes. The boardswere prepared in the same manner as previously in described in Example 2and further treated in the same manner as Example 9. The cubes wereprepared in the same manner as previously described in Example 1 andfurther treated in a manner similar to that used in Example 9. Except inboth cases, various different enhancing materials were used rather thanjust trimetaphosphate ion. Humidified sag deflection was measured in thesame manner as previously described in Example 2. Compressive strengthwas measured in the same manner as previously described in Example 1.

The results in Table 16 show that all materials tested that are withinthe definition of enhancing materials above, when used to treat set anddried calcium sulfate dihydrate cast, cause the resulting products toexhibit significant resistance to permanent deformation and significantincreased strength compared with the controls.

TABLE 16 Lab test results of post-treated gypsum cube (2 × 2 × 2)/board(24 × 6 × 0.5) cast from stucco with various phosphate & chlorideaddition Addition Dry Board Water Pick-Up Ten Day Compressive PhosphateSalts Or Level Weight from 90/90 Humidified Sag Strength Of OtherSpecified Chemicals (wt. %) (gram) Room (wt. %) Deflection (inches)Dried Cubes(psi) Sodium Trimetaphosphate 0.4 537.0 0.5 0.016 725 SodiumHexametaphosphate 0.4 538.2 0.9 0.019 697 Tetrapotassium Pyrophosphate0.4 538.7 0.3 0.017 Tetrasodium Pyrophosphate 0.4 556.2 0.6 0.011 SodiumAcid Pyrophosphate 0.4 542.1 0.4 0.012 Monosodium Dihydrogen Phosphate0.4 545.6 1.5 0.025 710 Monopotassium Dihydrogen Phosphate 0.4 487.5 0.20.029 708 Phosphoric Acid 0.4 534.7 0.4 0.065 624 SodiumTripolyphosphate 0.4 540.5 0.6 0.123 657 Boric Acid 0.4 486.6 0.1 0.345611 Control 0.0 543.9 0.2 0.393 576 Disodium Monohydrogen Phosphate 0.4541.3 0.7 0.674 724 Trisodium Phosphate 0.4 532.8 0.6 1.082 754Magnesium Chloride 0.4 559.9 2.3 1.385 567 Sodium Chloride 0.4 539.4 7.76.385 521

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it should be appreciated thatvariations and modifications can be effected within the spirit and scopeof the invention.

1-51. (canceled)
 52. A set gypsum-containing product prepared by amethod comprising forming a mixture of calcined gypsum, water, anaccelerator, and one or more enhancing materials chosen from the groupconsisting of: sodium trimetaphosphate, tetrapotassium pyrophosphate,tetrasodium pyrophosphate, aluminum trimetaphosphate, sodium acidpyrophosphate, ammonium polyphosphate having 1000-3000 repeatingphosphate units, and acids, salts, or the anionic portions thereof, andmaintaining the mixture under conditions sufficient for the calcinedgypsum to form an interlocking matrix of set gypsum, the enhancingmaterial or materials having been included in the mixture in an amountsuch that the set gypsum-containing product has greater resistance topermanent deformation than it would have if the enhancing material hadnot been included in the mixture, such that when the mixture is cast inthe form of ½ inch gypsum board, said board has a sag resistance, asdetermined according to ASTM C473-95, of less than about 0.1 inch pertwo foot length of said board, the accelerator having been included inan amount such that the set gypsum-containing product has greaterstrength than it would have if the accelerator had not been included inthe mixture.
 53. A gypsum board comprising a core of material sandwichedbetween cover sheets, wherein the core comprises an interlocking matrixof set gypsum, and the board has been prepared by a method comprising:forming or depositing a mixture between the cover sheets, wherein themixture comprises a calcined gypsum, water, an accelerator, and one ormore enhancing materials chosen from the group consisting of: sodiumtrimetaphosphate, tetrapotassium pyrophosphate, tetrasodiumpyrophosphate, aluminum trimetaphosphate, sodium acid pyrophosphate,ammonium polyphosphate having 1000-3000 repeating phosphate units, andacids, salts, or the anionic portions thereof, and maintaining themixture under conditions sufficient for the calcined gypsum to form theinterlocking matrix of set gypsum, the enhancing material or materialshaving been included in the mixture in an amount such that the gypsumboard has greater sag resistance than it would have if the enhancingmaterial had not been included in the mixture, said board having a sagresistance as determined according to ASTM C473-95 of less than about0.1 inch per two foot length of said board, the accelerator having beenincluded in an amount such that the gypsum board has greater strengththan it would have if the accelerator had not been included in themixture.
 54. The gypsum board of claim 53, wherein the concentration ofthe enhancing material in the mixture is from 0.004 to 2.0 percent byweight, based on the weight of the calcined gypsum.
 55. The gypsum boardof claim 53, wherein the calcined gypsum comprises one or more of:calcium sulfate anhydrite; calcium sulfate hemihydrate; or ions ofcalcium and sulfate.
 56. The gypsum board of claim 53, wherein theenhancing material comprises one or more of the following salts, or theanionic portions thereof: sodium trimetaphosphate and ammoniumpolyphosphate having 1000-3000 repeating phosphate units.
 57. The gypsumboard of claim 53, wherein the mixture comprises 0.02-1.5 weight percent(based on the weight of calcined gypsum in the mixture) of chloride ionsor salts thereof.
 58. The gypsum board of claim 53, wherein the mixturefurther comprises a pregelatinized starch.
 59. The gypsum board of claim53, wherein the concentration of the pregelatinized starch in themixture is from 0.08 to 0.5 percent by weight, based on the weight ofthe calcined gypsum.
 60. The gypsum board of claim 53, wherein: the corehas voids uniformly distributed therein; and the mixture furthercomprises an aqueous foam.
 61. The gypsum board of claim 60, wherein theaqueous foam has been formed from a foaming agent, or a blend of foamingagents, having the formulaCH₃(CH₂)_(x)CH₂(OCH₂CH₂)_(y)OSO₃ ⁻M⁺ wherein X is a number from 2 to 20,Y is a number from 0 to 10 and is 0 in at least 50 weight percent of thefoaming agent or blend of foaming agents, and M is a cation.
 62. Thegypsum board of claim 53, wherein the mixture further comprises apregelatinized starch and an aqueous foam.